Previously available electromagnetic actuators using a magnetic circuit are shown in FIGS. 8 and 9.
In the electromagnetic actuator depicted in FIG. 8, magnetic poles 3 are formed on the bent ends of iron core 2, around which coil 1 is wound. Permanent magnet 4 is placed in the center of the portion where the coil is wound around core 2. Permanent magnet 4 is supported by iron armature 5 in such a way that it is free to rotate. Magnetic poles 6, on either end of the said iron armature 5, face the magnetic poles 3 of the iron core.
The electromagnetic actuator shown in FIG. 9 has its magnetic poles 3 on the bent ends of iron core 2, around which coil 1 is wound. Between the two magnetic poles 3 of the core is placed permanent magnet 4, which has three point magnetized poles N-S-N (or S-N-S). The pole in the center of the said permanent magnet 4 supports iron armature 5, which has a projection 7 which acts as a fulcrum so that the iron armature 5 is free to rotate. The magnetic poles 6 on the ends of iron armature 5 face the magnetic poles 3 of iron core 2.
In the electromagnetic actuator shown in FIG. 8, permanent magnet 4 is placed on the portion of the core on which the coil is wound, so that the space for winding the coil is particularly limited in the miniature type of relay, in which the space is actually shorter than 2 centimeter. This decreases the number of turns by which coil 1 may be wound. Because permanent magnet 4 effectively divides in half the portion of the core on which the coil is wound, the wire winding equipment has to be more complex. In FIG. 8, the coil must be wound more slowly around the center portion of the core between the left and right portions of the coil, which increases the winding time. Since the wire is so thin (0.022-0.073 mm depending on the input voltage), the wire is also prone to break as it is led across the center of the core.
Because the electromagnetic actuator pictured in FIG. 9 requires a permanent magnet 4 which is point magnetized in three places, the material is limited to a relatively point magnetic type such as isotropic ferrite or ferric chrome cobalt. Also, the cost is driven up by the fact that it is difficult to magnetize the material once the actuator is assembled. In general, isotropic ferrite can make a unoriented magnet having a maximum magnetic energy content of approx. 6.5 (BH).sub.max kj/m.sup.3, and anisotropic ferrite can make a oriented magnet having a maximum magnetic energy content of approx. 25.0 (BH).sub.max kj/m.sup.3, which is stronger than that of the unoriented magnet.